The G-Factor method calculates amounts that can be safely withdrawn from a portfolio invested in the S&P 500 index, with the monthly withdrawal amount remaining level or increasing on an inflation-adjusted basis. Tested with U.S. stock market data since 1870, with any starting or ending date, there are many parameter sets that are stable during all historic periods. The approach also cannot be gamed. The withdrawal amount for a given current asset balance is the same regardless of when one began withdrawals, whether it was 1871, 1971, last year, or yesterday.